An ink jet printer (hereinafter referred to simply as “printer”) which is an example of a related-art printing apparatus includes a head having a plurality of ink discharging portions provided in a juxtaposed relationship thereon and each having a nozzle. Ink droplets are discharged from the ink discharging portions toward a printing object to form an image.
Here, the printing resolution of the head depends upon the juxtaposition distance of the ink discharging portions. For example, where the resolution is 300 dpi, the distance between the ink discharging portions is set to approximately 84.6 μm.
In addition to a case wherein a head of 300 dpi is used, for example, to print with a resolution of 300 dpi, also it is possible to print with another resolution equal to 1/n (n is a positive number) the original resolution of the head such as 150 dpi by thinning out the discharges of ink droplets from the ink discharging portions.
Or, if the head is moved by a plural number of times at the same printing position so that ink droplets are landed at distances equal to 1/n the distance between the ink discharging portions, then also it is possible to print with a resolution equal to n times the original resolution of the head such as, for example, 600 dpi or 1,200 dpi.
However, in the related-art described above, where the resolutions of print data and the printer do not coincide with each other, it is necessary to convert the print data into print data of the resolution of the printer by interpolation. However, the related-art described above has a problem that the conversion deteriorates the resolution.
FIG. 11A shows, in an enlarged scale, an image of 600 dpi and particularly shows white and black lines formed in a pitch of 42.3 μm. If it is tried to print the print data using a printer having a resolution of, for example, 720 dpi, then the image of 600 dpi is converted into another image of 720 dpi. However, upon such conversion, the resolution of the image deteriorates, and an image having a deteriorated resolution as shown in FIG. 11B is printed.
Further, in a printer which includes a serial head which successively discharges ink droplets while the head is moved in a widthwise direction of print paper, also it is possible to change the displacement amount of the head in the paper feeding direction to vary the resolution. However, the printer has a problem that, depending upon a required resolution, a very small displacement amount is required and a very long period of time is required for the printing. Further, a printer which includes a line head having ink discharging portions provided in a juxtaposed relationship over a substantially overall width of print paper has a problem that the resolution cannot be changed because ink droplets are merely discharged from ink discharging portions of the fixedly provided line head but the line head does not move in the widthwise direction of the print paper.